In this book, the genetic variability among Citrullus colocynthis, C. colocynthis var. colocynthoides and C. lanatus was illustrated based on the data obtained from karyotype analysis and electrophoretic patterns of seed storage proteins as well as three enzyme systems. In addition, the effect of different concentrations of 6-benzylaminopurine either alone or in combination with naphthalene acetic acid on the morphogenetic response of cotyledon and zygotic embryo explants of the studied plants was tested. The biomolecular changes during in vitro organogenesis of studied Citrullus spp. were investigated. Finally, an efficient protocol for isolation and fusion of protoplasts of studied Citrullus spp. was achieved.